Type Ib and Ic supernovae

These stars have shed or been stripped of their outer envelope of hydrogen, and, when compared to the spectrum of Type Ia supernovae, they lack the absorption line of silicon.

[6] As Type Ib and Ic supernovae age, they also display lines from elements such as oxygen, calcium and magnesium.

[7] Prior to becoming a supernova, an evolved massive star is organized like an onion, with layers of different elements undergoing fusion.

Thus when the outer envelope of hydrogen is shed, this exposes the next layer that consists primarily of helium (mixed with other elements).

[8] Type Ib and Ic supernovae are hypothesized to have been produced by core collapse of massive stars that have lost their outer layer of hydrogen and helium, either via winds or mass transfer to a companion.

[6] The progenitors of Types Ib and Ic have lost most of their outer envelopes due to strong stellar winds or else from interaction with a close companion of about 3–4 M☉.

[9][10] Rapid mass loss can occur in the case of a Wolf–Rayet star, and these massive objects show a spectrum that is lacking in hydrogen.

The Type Ib supernova SN 2008D [ 1 ] [ 2 ] in galaxy NGC 2770 , shown in X-ray (left) and visible light (right), at the corresponding positions of the images. ( NASA image.) [ 3 ]
The onion-like layers of an evolved, massive star (not to scale).